The goal of this project is to specify the roles of endogenous mammalian bombesin-like peptides in the peripheral (gastrointestinal) generation and in the central neural processing of the physiological satiety signals which serve (a) to limit meal size and (b) to determine the length of the postprandial intermeal interval in the rat. The sequence of experimental steps to achieve this goal will be as follows: 1) Determine the sites of action of exogenous, peripherally-administered bombesin (BBS)-like peptides when they limit meal size and prolong the postprandial intermeal interval; (2) Determine the pathways to the central nervous system for these two effects; (3) Determine if peripheral, endogenous BBS-like peptides are necessary for the complete expression of these two effects; (4) Determine if intracerebral microinjections of exogenous BBS-like peptides produce behaviorally specific satiety effects on meal size and on the postprandial intermeal interval; (5) Determine if the action of BBS-like peptides at these brain sites is necessary for the two satiety effects of exogenous, peripherally-administered BBS-like peptides; (6) Determine if the action of two-endogenous BBS-like peptides at these brain sites is necessary for the two satiety effects of ingested food, on meal size and on the postprandial intermeal interval. If the bombesin family of peptides is shown to play roles as physiological mechanisms of postprandial satiety at peripheral and/or central sites, this result will have fundamental implications for the analysis of normal feeding behavior and for the determination of the pathophysiology and treatment of the two major satiety disorders in humans, bulimia nervosa and obesity.